1. Field of the Invention
This invention relates to a machine tool, and more particularly to a numerically controlled wood working machine wherein several working heads such as a router head, a drill head, a grinder head and a planer head are selectively used for various working operations.
2. Description of the Prior Art
One of wood working apparatus of the type mentioned has been provided already by the inventor and is disclosed in Japanese Patent Publication No. 33281/1984. The apparatus includes a ram mounted for upward and downward sliding movement on a vertical rail provided on a front face of a center column. The ram is moved upwardly or downwardly by means of a screw shaft connected to be rotated by a motor. A pair of beams extend horizontally leftwardly and rightwardly from the opposite left and right sides of the center column. The beams are separated from each other on the opposite sides of the ram and define a fixed gap therebetween. Each of the beams has a pair of upper and lower horizontal rails provided in parallel to each other thereon while a pair of short upper and lower horizontal rails are provided on a front face of the ram such that, when the rails on the ram are positioned in level with the rails on the left and right beams, the rails on the left and right beams are connected to each other by way of the rails on the ram.
Five head holders are mounted for leftward and rightward sliding movement in a horizontal row on the upper and lower rails and individually extend in vertical directions. When the rails on the left and right beams are connected to each other by way of the rails on the ram, the head holders can move leftwardly and rightwardly between the left and right beams. Meanwhile, only one of the five head holders is permitted to be positioned on the ram in the gap between the left and right beams, and such head holder can be moved upwardly or downwardly by and together with the ram. A head base is mounted for adjusting movement in a vertical direction on a front face of each of the head holders, and one of such working heads as mentioned hereinabove can be selectively attached to the head base so that, when the head holder is moved upwardly or downwardly, the working head is moved upwardly or downwardly together with the head holder. Thus, a selected one of working heads is attached to each of the head bases on the head holders. The ram can thus removably carry a single working head thereon by way of a corresponding head holder. The ram has a connector by way of which power is supplied only to a working head carried on the ram then. Consequently, only a working head carried on the ram can be moved up and down together with the ram, and a motor for the working head is energized to drive the working head to perform a working operation.
A pair of left and right hydraulic cylinder devices are supported horizontally on the left and right beams, respectively. The hydraulic cylinder devices have piston rods which hold the five base holders therebetween and slidably move, when the hydraulic cylinder devices are energized suitably, the five base holders simultaneously in the leftward or rightward direction. In order to position a selected one of the five working heads in the gap between the left and right beams so that it may be carried on the ram, a plurality of stopping electromagnets are secured in a predetermined spaced relationship in the leftward and rightward directions on each of the left and right beams such that plungers thereof may stop sliding movement of the head holders. A similar stopping electromagnet is secured also to the ram.
The wood working apparatus, however, are disadvantageous in the following points.
In particular, depending upon contents of working operations, a particular one of working heads may be used very frequently while another particular working head is used seldom. However, when a working head which is used frequently is to be exchanged, also another working head which is used seldom must be moved leftwardly or rightwardly together with the former working head, which is inefficient and uneconomical and is not suitable for working for the production of many kinds of products by small amounts.
Further, when a working head is to be exchanged, all working heads must be moved simultaneously irrespective of a difference in frequency of use as described above. Since power required for such movement increases as the number of working heads increases, the number of working heads which can be used is limited naturally.
Besides, in order to allow selection of an arbitrary one of a plurality of working heads, two hydraulic cylinder devices and a large number of stopping electrodes are required. Accordingly, a comparatively great number of parts are required and the structure is complicated, which requires a correspondingly high production cost.
Further, when a plurality of head holders are to be slidably moved simultaneously, the head holders are held between piston rods of a pair of left and right hydraulic cylinder devices, and the hydraulic cylinder devices are alternatively rendered operative. Meanwhile, in order to position the working heads, stopping electromagnets are selectively energized or deenergized to stop sliding movement of the head holders by means of plungers thereof. Accordingly, control of a hydraulic pressure is difficult, and accurate positioning cannot be attained.
Moreover, since a plurality of head holders are contacted with each other and held between and moved by piston rods of a pair of left and right hydraulic cylinder devices, if it is intended to use a working head which has a greater width than a head holder, a spacer or spacers must be interposed between the head holder and an adjacent head holder or holders so that the head holders may not interfere with each other. Besides, the position or positions of a stopping electromagnet or electromagnets must be changed correspondingly, which is cumbersome.
In addition, if the number of head holders is changed, also specifications of hydraulic pressure control of hydraulic cylinder devices must be changed.